1. Field of the Invention
The present invention relates to an encrypting method and apparatus, a decrypting method and apparatus, and a recording medium in which information encrypted by an encrypting method or an encrypting apparatus is recorded; and more particularly to an encrypting method and apparatus, a decrypting method and apparatus, and a recording medium suitable for use in a system in which information such as video signals, audio signals, data signals or the like is encrypted, the encrypted information is recorded on a recording medium, and the encrypted information is decrypted.
2. Description of the Related Art
Typically when information is encrypted for recording on a recording medium, the information is encrypted by using a predetermined encryption key. The encrypted information is decrypted by using a decryption key.
Two known types of cryptosystems which employ a key (an encryption key) include: a common-key cryptosystem and a public-key cryptosystem. In the common-key cryptosystem, a key (encryption key) used upon encryption is the same as a key (decryption key) used upon decryption. Frequently a data encryption standard (DES) is employed in common-key cryptosystems. On the other hand, in public-key cryptosystems, the encryption key and the decryption key are different from each other. In public-key cryptosystems, it is common to open the encryption key to the public, while the decryption key is kept secret. In general, such encryption methods and decryption methods are known.
An encryption method is disclosed in Japanese patent publication No. 60007/1990. According to the method, an encryption key is generated based on a data forming a file to be recorded on a recording medium. Information is encrypted by using the encryption key, and the encrypted information is recorded on the recording medium. The file is reproduced from the recording medium, and a decryption key is generated based on data forming the file. Then, the encrypted information is decrypted by using the generated decryption key.
However, when such encryption and decryption methods are employed, the file used for generating the encryption key is recorded on one portion (sequent regions) of the recording medium, which may allow the file to be duplicated with comparative ease.